Transvenous temporary pacing, much less painful than the transthoracic
method, is required for many indications such as a bridge to
permanent pacing, especially for patients who are unable to
undergo immediate permanent implantation or for patients whose
bradycardia is severe and hemodynamically (blood pressure, pulse
rate) unstable. It is required most often in patients with severe
infranodal block and less frequently with AV nodal block and
sick sinus syndrome (see figures 16, 17). It may be required
to treat significant bradycardia due to drugs such as an excess
of digitalis. Anticipated or actual bradyarrthythmia during
acute myocardial infarction also may require temporary pacing.
The onset of a right bundle branch block (RBBB) of the cardiac
conductive system (see figure 104B) may precede infranodal block.
An abrupt change may occur from 1:1 conduction to Mobitz II
second degree block (see figure 17) or complete asystole. The
lack of an escape rhythm makes the above possibilities dangerous
and warrants temporary pacing, even with only the onset of RBBB
in the presence of an acute anterior myocardial infarction.

Temporary
pacing of either atrium or ventricle frequently is useful after
cardiac surgery, since transient bradyarrhythmias and atrial
flutter (see figures 5A, 5B) are common. Also, it can be used
in recurrent tachyarrhythmias like torsades de pointe (see figure
13) and incessant ventricular tachycardia (see figure 12).

As
in permanent pacing each system requires leads and a pacing
generator. Standard transvenous pacing leads are inserted percutaneously
into femoral, internal, jugular, or subclavian veins, usually
under flouroscopic control.

Permanent
Pacing

Pacing
in Congenital Atrioventricular Block

Congenital heart block is usually due to AV nodal block. Patient
tend to be asymptomatic and typically have narrow QRS complex
rhythms. However, congenital AV block is associated
with serious and possible fatal complications, including syncope
and sudden death.In one .study, a mean daytime heart rate
less than 50 beats per minute was associated with sudden death
or need for pacemaker. Exercise testing is useful to assess
response at rest and exercise.Other indicators of poor
outcome include prolonged QT interval (corrected for heart rate),
cardiomegaly. atrial enlargement. decreased left ventricular
systolic function, mean ventricular rates lower than median
for age,periods of junctional exit block, and mitral regurgitattion.
5 52 who do not rpolnr,~ ~ ~ A ~ ~